3gb of RAM being seen as 2gb on OSx - Mac Pro

I have a first gen 2.66 Mac Pro with 10.5.5. I have had 3gb of RAM installed for over a year. Just recently I noiced system info shows I have only 2gb of RAM installed. It shows I have 4 slots of 512mb installed.. however 2 of those are 1gb each. It used to show 3gb but now recognizes my two 1gb sticks as 512mb.

I just opened my Mac and double checked the RAM. All 4 slots on the top board are full and slots 3/4 have 1gb Transcend RAM. These are Mac Pro compatible modules.. and like I said they used to work.

So what would cause OSX to see 1gb as 512mb? Could the RAM be bad?

Thanks in advance.

Edit: I have been reading around online about Parallels causing some system issue of max RAM limits. I had parallels installed awhile ago and (tried) to remove it via Spring Cleaner. Maybe this is related?

Have you run Apple Hardware Test? Two of my 2GB modules recently showed as 1GBs. I ran AHT and got errors.

You have all your RAM on Riser A? FWIW the Memory Configuration Chart has 2 1GBs on Riser A, and the 2 512GBs on Riser B. (I don't know which generation of Mac Pro the chart was made for.)

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I can't run the hardware test. I am using a retail Leopard DVD.. hold down D on boot and it just slowly boots straight to the OS. You said AHT gave you errors.. what was the solution or result? I did run a memory test with Tech Tools Pro and everything passed.

I also moved the 1gb sticks to the bottom slot. So now I have 2 on top and 2 on bottom. The results are the same.

I also removed the stock 2x512 sticks from Apple and just put my 2x1gb sticks in and OSx only reads 1gb total. XP from bootcamp also only reads 1gb total when I have 2gb installed.

At this point it seems like maybe the RAM is just bad? Wouldn't bad RAM not work at all as opposed to loading up at half size?

Originally riser A had the stock 2x512mb in slot 1/2. When I first installed the additional 2x1gb they went into slots 3/4 of riser A. Since then, I have put the 2x1gb RAM on Riser B 1/2. I have also switched the stock ram to riser B and 1gb sticks to riser A each on slot 1/2. Still no luck.. I even let the 2x1gb sticks cool down thinking maybe it was a heat related issue but still no luck.

Originally riser A had the stock 2x512mb in slot 1/2. When I first installed the additional 2x1gb they went into slots 3/4 of riser A. Since then, I have put the 2x1gb RAM on Riser B 1/2. I have also switched the stock ram to riser B and 1gb sticks to riser A each on slot 1/2. Still no luck.. I even let the 2x1gb sticks cool down thinking maybe it was a heat related issue but still no luck.

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Don't you need to alternate the pairs on each riser? Basically, you should have both your risers laid out the same way. One 512 and one 1 gig on each riser in the same positions.

You should have the 2 1GB on riser A and the 2 512s on riser B. If this does not work, and from what you have said, it sounds like it isn't, I am guessing that one of your Transcends is bad and the OS is somehow seeing that there are two installed but only can access 1GB RAM so it thinks there are two 512s in there??? If you put the 2 sticks of 1GB in the first two slots of Riser A by themselves and it still only recognizes 1 GB instead of two, I can't think of anything else except one of them is bad.

I am guessing that one of your Transcends is bad and the OS is somehow seeing that there are two installed but only can access 1GB RAM so it thinks there are two 512s in there??? If you put the 2 sticks of 1GB in the first two slots of Riser A by themselves and it still only recognizes 1 GB instead of two, I can't think of anything else except one of them is bad.

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Yeah it must be something weird like that. Should I keep using it? I think I will just order a new 2x2gb set in January and toss this bad 1x1gb out. At least it kind of works until then lol.

Well some good news (kind of). My co-workers also has a 2.66 Mac Pro and it reads the RAM exactly the same. So it sounds like the memory is bad and the Mac is fine.

Yeah it must be something weird like that. Should I keep using it? I think I will just order a new 2x2gb set in January and toss this bad 1x1gb out. At least it kind of works until then lol.

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Please keep in mind everything below here is based on my limited experience/knowledge and is speculative. Having said that....

I think you are probably OK to use the RAM for the time being since your system is recognizing the RAM as two 512s, but you should upgrade/replace as soon as possible. I am assuming that your computer will never actually try to access the RAM on that second stick of 1GB, though. If it ever tries to access that second, faulty 1GB, though, your computer will likely freeze and/or crash.

Again, lots of guessing here, so get some new RAM as soon as you can.

What I would try to do is get some new 2GB RAM pairs and also contact Transcend for a replacement. Check Newegg , got myself some 2x2GB iRam that seems to work pretty well aned was around $100 for the pair. Worse case scenario, you've upgraded to 5GB RAM, best case scenario and you get workable replacements from Transcend, you'll be running 7GB.

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